Modulator system



Patented Feb. 7, 1933 UNITED STATES" JOHN AQWILIQOUGHBY, or CAMBRIDGE,MASSACHUSETTS MODULATOR SYSTEM Application filed December 18 1928.Serial No, 326,880.

My invention relates to modulator systems 1n general and morespecifically to modulator systems employed in high frequency signalmg V5 object of my invention isto provide a combination oscillator andmodulator system wherein a single thermionic tube is employed. Anotherobject of my invention is to provide a combination oscillator andmodulator system wherein the'frequency of the oscillatory circuit issubstantially uniform irrespective of modulation.

Still another object of my'invention is to 7 provide a single thermionictube having associated circuits for the generation and modulation ofhigh frequency electrical energy. Other and further objects of myinvention reside in the circuit arrangements I employ, a betterunderstanding of which can be had by referring to the specificationfollowing and to the accompanying drawing which is a schematic circuitdiagram showing the modulator system of my invention.

In high frequency signaling systems and especially in high frequencysignaling systems wherein programs of speech and music are broadcast itis necessary that the modulating system be of the proper design tofaithfullyand adequately modulate the carrier energy. The generallyemployed methods for modulating the carrier energy :are well known tothose experienced in the art. A lower frequency is superimposed upon thehigher frequency and produces side bands. As an illustration, thecarrier energy may have a frequency of 500 kilocycles. The side bands ofmodulation will be generally or minus a given frequency band of this500kilocycle frequency.- This is generally accomplished by controlling theinput energy to the thermionic tube generator in accordance with thelower or audio frequency. Subsequent amplifiers or precedent modulatorsand amplifiers usually destroy or distort some of the desired audiofrequency varia tions of'e'lectrical energy and hence the receivedenergy is not a like representation of the original audio frequencyvariations. This is generally referred" to as cutting off certaindesirable frequencies which should connected with a with ammeter 13.Chok plus but do not modulate the carrierenergy. The modulator systemofmy invention avoids many disadvantages of other systems and provides ameans for efliciently and effectively modulating the carrier energy instrict accordance-with the audio frequency energy.

he accompanyingdrawing is a schematic circuit diagramshowing themodulator system of my invention. Thermionic tube 1 is of the typehaving a cathode 2, inner. grid 59 electrode3, anode 4 and outervgriolelectrode 5. v In the circuit here described, the inner grid 3;maybe referred to as the control grid electrode, and outer grid 5 may bereferred to as the auxiliary grid electrode. Cathode 2 is energizedbytransformerfi and the latter is source of alternating current. Apositive potential is applied to anode 4 from source 7; A potential ofsuitable value and polarity is pply to control grid 3 a potentialnegative with respect to cathode 2 which will be suitable for operationin many cases, A mechanically 7'5 vibratile element '9 is connected tocontrol electrode 3' and cathode 2. Mechanically vibratile element maycomprise a quartzor other crystal having piezoelectric properties or maybe any suitable frequency stabilizing means. Anode 4 isassociated.withji-nductance 11 by means of capacity 10. "The latter prevents theshortcircuiting of source 7. Inductance 11 is shunted by capacity12inseries V e coils I5, 16,, ,18 and 19 are adapted to exclude highfrequency energy from sources 8, and-transformer B. A connection 20 fromthe electrical center of the secondary of transformer 6, provides acommon return path to cathode 2. Auxiliary electrode 5' is connectedtothe common return circuit of cathode2 through winding 21 oftransformer22 and in series with the independent source of energy 26.There is thus applied to auxiliary grid 5, a potential which willusually be positive with respect 'to the cathode, 'in operation.Asou-rc'e of energy 23 is connected in series with microphone art-andwinding 25 of transformer 22. Microphone 24 may be replaced by anysource-of current applied to inner grid 3 from 770 source 8. 'As sown inthe drawing, source 8 may conveniently be connected to a variations or avariable resistor such as a photoelectric cell.

In an operation the electrons emitted by cathode 2 are attracted toanode 1. This force of attraction is not perfect however and a spacecharge immediately adjacent to anode l exists. 'Auxiliary electrode!) isplaced in this position and exerts a predominate infiuence upon thespace charge. Control electrode 3 functions in the usual manner andconstitutes a part of the capacity for feeding back the energy from theanode circuit. The oscillations of energy are sustained by element 9when the energy fed back from the anode or output circuit is of afrequency approximately corresponding-to the frequency characteristicsof element 9or a multiple frequency thereof. Variations in theresistance of microphone 24 cause variations of the current in Winding25, which variations cause variations of potential in winding 21.Variations of potential in winding 21 cause variations of' potentialsupplied auxiliary electrode 5'. The potential of electrode 5 exerts amarked influence on the electronic stream, increasing ordecreasing thenumber of electrons reaching anode fl in accordance with variations ofthe potential. Variations of the electronic stream between cathode 2 andanode l effect like variations of current in the output circuit tube'l.The percentage of the carrier subjected to modulation may be easilyregulated. A relatively low current is ordinarily present in the circuitincluding auxiliary electrode 5 and the common connection to cathode 2.This; relatively low current is especially desired and makes possiblethe complete control of the carrier in accordance with the low frequencyvariations. v lMany modifications of my invention are possible withoutdeparting from the spirit of my invention. Succeeding amplifiers may beassociated with the output circuit and caused to amplify theenergybefore the same is'radiated or transmitted over a wired radio circuit.The modulator system of my inven- "tionconstitutes an eiiicient masteroscillator for exciting additional amplifiers. Because of the smallamount of current in the auxiliary electrode circuitthe output energy ofa thermionic tube of high power may be easily andcompletely modulated.Mechanically vibratile element 9 may be of any suitable design adaptedto sustain oscillations and havinga capacity to withstand the'value ofenergy to which it is subjected.

While I have shown a piezo electric crystal element in the circuitarrangementof my 11 1:: be understood that vention, I desire that itthis element may be replaced by a mechanical oscillator composed ,ofmetal or alloys such as nickel, and other metals which when influencedby alternating current will exhibit 'lations, an'independent source ofouter gri or anode circuit of thermionic P such manner that a negativecathode, a .piezo electric crystalelement connected in the otherdetermined frequency,

magneto strictive properties which in turn will hold the frequencyconstant.

I realize that many modifications of the modulator system of myinvention are possible wherein the oscillator and modulator are combinedin a single thermionic tube and it is to be-understood that theembodiments of my invention are not to be limited to thespecificarrangement shown in the accompanying drawing and described inthe foregoing specification but only as defined by the scope of theappended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

-' 1. In an electron tube modulatingzand generating system, an electrontube having cathode, anode, inner grid and outer grid, independentcircuits connecting said inner gri to said cathode, one of said circuitsforming a path forhigh frequency'oscillationls, another of saidcircuitsforming a path for direct current biasing potential, anelectromechanical vibratordisposedin said first mentioned circuit, anoutput circuit comprising a source of positive anode potential connectedbetween said anode and said cathode, an input transformer having itsprimary connected .to a source of voice-frequency oscilotential, saidouter grid being connected to said cathode through the secondary of saidtransformer and said source oflouter grid potential connected in seriesin such manner that a positive vpotential'is applied to said outer gridwithqrespectto, said cathode. 2

2. In an electron'tub'e modulating and generating system, an electrontube having cathode, anode, inner grid and outer grid, a pair ofcircuits interconnecting-- said cathode and 1 inner grid, asource ofinner grid biasing potential connected in one of said circuits in biasis applied to said inner grid with reference to said of, said circuitsfor sustaining oscillations in said system at aprean output circuitcomprisinga source of positive anode potential connected between saidanodeand said cathode, an input transformer having its primary connectedto a source ofvoice-frequencyoscillations, an, independent source ofouter grid potential, said outer grid being connected tosaidcathodethrough the secondary of said transformer and said source ofouter grid potential connected 9111 series in such manner that apositive potential is applied to said outer grid wi h respect to'saidcathode. i I

3. In an'electrontube modulating and gen- ,eratingsystem, anelectrontube having cathode, anode, inner, grid and outer grid, a pair of branchcircuitsconnecting' sald lnner grid to saidcathode, ;a frequencyfcontrolelement connected between said inner grid and said cathode, in one ofsaid branch circuits, a source of biasing potential for said inner gridconnected in the other of said branch circuits an output circuitcomprising a source of positive anode potential connected between saidanode and said cathode, an input transformer having its primaryconnected to a source of voice-frequency oscillations, an

independent source of outer grid potential,

said outer grid being connected to said cathode through the secondary ofsaid transformer and said source of outer grid potential connected inseries in such manner that a positive potential is applied to said outergrid with respect to said cathode.

4. In an electron tube modulating and generating system, an electrontube having cat-hode, anode, inner grid and outer grid, a source ofinner grid biasing potential connected between said inner grid and saidcathode in such manner that a negative bias is applied to said innergrid with reference to said cathode, a piezo electric crystal elementconnected between said inner grid and said cathode and in parallel withsaid source of inner grid biasing potential, an output circuitcomprising a source of positive anode potential connected between saidanode and said cathode,

an input transformer having its primary connected to a source ofvoice-frequency oscillations, an independent source of outer gridpotential, said outer grid being connected to said cathode through thesecondary of said transformer and said source of outer grid potentialconnected in series in such manner that a positive potential is appliedto said outer grid with respect to said cathode.

In testimony whereof I aflix my signature.

JOHN A. WILLOUGHBY.

